A venetian blind is a window covering unit having a plurality of vertically stacked, horizontally rotatable slat-like members constructed of wood, metal or plastic. The blind is provided with certain cords for raising the slats and ladders for tilting the slats to any desired angle to control the amount of light that can pass through the blind.
Although earlier in the art it was customary to adjust slat angle by hand manipulation of the ladders which interconnected with the slats, it is now customary to provide a single control lever or wand which is typically rotated about its longitudinal axis to perform the slat angle adjustment. It has also been customary for the slat angle control lever to be capable of being operated even after the slats had reached a maximum angular relationship which frequently resulted in destruction or impairment of the control lever mechanism. To prevent damage to the slat control apparatus as well as possible breakage of the ladders interrelating the slats, there are known devices to minimize or alleviate this problem by providing a relative complicated and expensive slip clutch arrangement, such that when the retarding force reaches a certain maximum the device can be operated further without driving effect on the slats and associated ladders.